I'm a bit late to the party, but on the topic of message boxes I've found another potential bug (Windows 7):

The love.window.showMessageBox seems to cut off the last character in a string in the 'message' field. However, when using a 1 or 0 integer variable in the 'message' field, it shows that single digit fine.

It seems in demetris135's post that this doesn't happen when the box contains buttons? (also on Windows 7, unless this is somehow specific to me)

I also tested the box staying on top functionality, and it doesn't appear to work for me either.